1. Field of the Invention
The present invention relates generally to a solid state gamma camera module and an integrated thermal management method, and more particularly to a module and method for removing heat generated by integrated circuits while reducing heat flow to temperature sensitive CZT material.
2. Description of the Background Art
Radiographic imaging is the detection of radiation from a distributed radiation field in order to form an image. By detecting the amount of radiation emanating from a test subject, the resultant image may give a representative view of the structure of the test subject.
Radiographic imaging typically employs gamma rays. Gamma rays are a form of radiation that is emitted by excited atomic nuclei during the process of passing to a lower excitation state. Gamma radiation is commonly used for medical imaging, and is capable of passing through soft tissue and bone. Gamma radiation may be provided by a radiopharmaceutical, such as thallium or technetium, for example, that is administered to the patient. The radiopharmaceutical travels through the patient's body and may be chosen to be absorbed or retained by an organ of interest. The radiopharmaceutical generates a predictable emission of gamma rays through the patient's body that can be detected and used to create an image.
A radiographic imaging device may be used to detect radiation emanating from the patient and may be used to form an image or images for viewing and diagnosis. Conventional gamma cameras utilize a scintillation crystal (usually made of sodium iodide) which absorbs the gamma photon emissions and emits light photons (or light events) in response to the gamma absorption. An array of photodetectors, such as photomultiplier tubes, is positioned adjacent to the crystal. The photomultiplier tubes receive the light photons from the crystal and produce electrical signals having amplitudes corresponding to the amount of light photons received. The electrical signals from the photomultiplier tubes are applied to position computing circuitry, wherein the location of the light event is determined, and the event location is then stored in a memory, from which an image of the radiation field can be displayed or printed.
Also known in the art are solid-state nuclear imaging cameras, see, e.g., U.S. Pat. Nos. 4,292,645 and 5,132,542. Such cameras use solid-state or semiconductor detector arrays in place of the scintillation crystal and photomultiplier tubes. In a solid-state camera, gamma rays are absorbed in a semiconductor material, creating electron-hole pairs in the semiconductor material. A bias voltage across the semiconductor detector causes the electrons and holes to form an electric current through the semiconductor material. The currents are converted by associated circuitry into electrical signals, which are processed to determine the location and magnitude of the gamma ray absorption event.
While solid-state cameras offer potential benefits over the conventional scintillation crystal cameras in terms of reduced weight, improved resolution, improved uniformity and increased imaging area, the use of such cameras has presented its own set of problems. In particular, early solid-state detectors made of germanium had to be cryogenically cooled to achieve acceptable performance.
Semiconductor detectors made of cadmium zinc telluride (CZT) have recently been proposed for use in solid-state gamma cameras. Such detectors may be operated at room temperature.
A number of radiographic sensor device modules may be tiled in an array to form a detector head. The detector head may be formed such that the radiographic sensor modules are individually detachable for maintenance, adjustment, etc.
Power dissipation of wire bonded/die bonded integrated circuits produces undesirable heat in a radiographic sensor device (i.e., heat generated when integrated circuits are die bonded). This leads to several problems in a radiographic sensor device. For example, the heat may degrade the sensor efficiency. A sensor at elevated temperature is not as sensitive and is less able to detect extreme high or low levels of radiation from the subject. In addition, sensor heating may cause mechanical defects, such as warping or expansion and contraction of the sensor material, with resulting cracking or other mechanical failures.
Conventional methods for extracting heat use one or more of the following means of thermal conduction: (1) air, (2) conformal integrated circuit coating, (3) thermal connection point to the top surface of the integrated circuit, or (4) printed circuit board (PCB) material. These methods, however, have high thermal resistance between the integrated circuits and a heat sink interface, thereby increasing the CZT operating temperature and associated bulk leakage current.
Therefore, there remains a need for an improved solid state gamma camera module and integrated thermal management method that provides a low thermal resistance path between the integrated circuits and a heat-sink interface while reducing the heat conduction path to temperature sensitive CZT material.